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In the mountains of Central America, lives a little known creature called Alston's mice singer. This rodent, who spends his life circling the cloud forest, may not feel like he has a lot to tell us about ourselves.
But the mouse produces remarkable songs, and the researchers have found deep similarities to our own conversations. This ability can be linked evolutionarily to the ancient roots of human language.
Scientists have been fighting for more than a century to determine the origin of language in our mammal ancestors.
"Until very recently there was still this belief that human speech and mammal vocalizations are two completely different things, "said Steffen R. Hage, a neurobiologist at the University of Tübingen in Germany.
No other mammal has a brain capable of doing what is necessary for human language – from understanding the rules of grammar to coordinating fast and complex controls for the muscles of the mouth and throat.
Early studies suggested that mammals used much simpler brain circuits to communicate.
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If a monkey were to be confronted with another monkey, it was thought, the brain fear treatment centers would report a group of neurons in the brain stem. The brainstem then sends commands to the mouth and throat to produce a call.
But it turns out that monkeys can control their sounds in a way that early researchers have not recognized. Scientists can train monkeys to call only when they see a signal on a computer screen, for example. To exercise this control, monkeys use clusters of neurons located in the outer layer of the brain, called the cerebral cortex.
We have similar brain groups and they are essential to language. This resemblance between humans and monkeys means that the constitutive elements of language have evolved in our distant primate ancestors.
When scientists looked at mice – far more distant than monkeys, of course – they found no evidence of this type of control. The domestic mouse, the scientists' favorite species, produces simple ultrasonic squeaks.
In 2011, Michael A. Long, Neuroscientist, N.Y.U. The medical school, for the first time, heard Alston's mice singing and understood that, when it comes to sound, they are much more interesting than laboratory mice. The singing mice produce strong peeping tunes lasting up to 16 seconds, and each mouse produces its own distinctive song.
"It's their bar code that says," It's me, "said Dr. Long.
"They are kind of divas."
Michael A. Long
N.Y.U. Medicine School
Alston's singing mice sometimes sing a song when they are alone, but they are particularly vocal when other mice are present. Men sing as a way to fight the territory with other men, and men and women sing during the courtship.
Working with Steven M. Phelps, a biologist at the University of Texas at Austin, Dr. Long has set up a house for mice in his lab to study their brains.
"These are kinds of divas," he says. "They need exercise equipment in their cages and specialized diets. But they thrive here.
One day, Dr. Andrew M. Matheson, a graduate student of Dr. Long, noticed something weird about two male mice in nearby cages. Instead of singing on each other, they sounded like they were talking.
Dr. Long and his colleagues finally discovered that Matheson's intuition was correct. The singing mice never overlap: each mouse waits for the other one to stop, then start in a split second.
"They are polite in the conversation," said Arkarup Banerjee, a postdoctoral researcher in Dr. Long's lab.
For Dr. Long, these models were surprisingly similar to human conversation. "We are ready to be outstanding communicators," he said. "It's like hitting a tennis ball just over the net, back and forth. And neuroscience did not understand how the brain does that. "
The researchers began to probe the brain of mice, looking for the neurons that led them to be "polite" storytellers.
In one experiment, the researchers cooled a few degrees of mouse brain patches, which slowed the neurons. Scientists have discovered that a patch in the mouse's cortex is essential to control their singing. If this section is chilled, the mouse sings extended songs, adding additional notes.
The researchers also injected nerve blocking substances into this brain patch and then broadcast the recording of another man. Drugged men often omitted to sing. And when they did, they were slow to start, taking a few seconds to start their own song.
Dr. Long believes that this region of the mouse cortex is crucial for the special communication of the mouse. "We see him as an orchestra conductor," he said. "This allows animals to sing in this way in turn."
The study was published Thursday in Science. Dr. Hage, who did not participate in the research, said the results were both surprising and compelling.
They show for the first time that mammals other than primates can use the cerebral cortex to control their sounds. In addition, Dr. Hage added, the results raise the possibility that the common ancestor of humans and rodents, who lived about 100 million years ago, already possessed this ability.
"This is a characteristic that ultimately is crucial for the evolution of human language," said Dr. Hage.
Experience has shown Mr. Long that there are risks that depend too much on a type of mouse while ignoring the rest of the biodiversity. "This exposes the main blind spot to bet everything on a single species," he said.
It is possible that the circuits of Alston's singing mice and humans are so similar that they are influenced by the same genes. This can give mice good models to study how autism causes people to have difficulty with conversations – what Dr. Long describes as "a black box".
Dr. Long is now speaking to Alston's genetically engineered mice, with some of the mutations associated with autism.
"We will try to understand how they affect communication in a simpler system so that we can get to the heart of what is really happening," he said.
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